1. Field of the Invention
The present invention relates generally to eyeglass lenses. More particularly, the invention relates to a lens forming composition, system and method for making photochromic, ultraviolet/visible light absorbing, and colored plastic lenses by curing the lens forming composition using activating light.
2. Description of the Relevant Art
It is conventional in the art to produce optical lenses by thermal curing techniques from the polymer of diethylene glycol bis(allyl)-carbonate (DEG-BAC). In addition, optical lenses may also be made using ultraviolet (xe2x80x9cUVxe2x80x9d) light curing techniques. See, for example, U.S. Pat. Nos. 4,728,469 to Lipscomb et al., 4,879,318 to Lipscomb et al., 5,364,256 to Lipscomb et al., 5,415,816 to Buazza et al., 5,529,728 to Buazza et al., 5,514,214 to Joel et al., 5,516,468 to Lipscomb, et al., 5,529,728 to Buazza et al., 5,689,324 to Lossman et al., 5,928,575 to Buazza, 5,976,423 to Buazza, 6,022,498 to Buazza et al. and U.S. patent application Ser. Nos. 07/425,371 filed Oct. 26, 1989, 08/439,691 filed May 12, 1995, 08/454,523 filed May 30, 1995, 08/453,770 filed May 30, 1995, 08/853,134 filed May 8, 1997, 08/844,557 filed Apr. 18, 1997, and 08/904,289 filed Jul. 31, 1997, all of which are hereby specifically incorporated by reference.
Curing of a lens by ultraviolet light tends to present certain problems that must be overcome to produce a viable lens. Such problems include yellowing of the lens, cracking of the lens or mold, optical distortions in the lens, and premature release of the lens from the mold. In addition, many of the useful ultraviolet light-curable lens forming compositions exhibit certain characteristics that increase the difficulty of a lens curing process. For example, due to the relatively rapid nature of ultraviolet light initiated reactions, it is a challenge to provide a composition that is ultraviolet light curable to form an eyeglass lens. Excessive exothermic heat tends to cause defects in the cured lens. To avoid such defects, the level of photoinitiator may be reduced to levels below what is customarily employed in the ultraviolet curing art.
While reducing the level of photoinitiator addresses some problems, it may also cause others. For instance, lowered levels of photoinitiator may cause the material in regions near an edge of the lens and proximate a gasket wall in a mold cavity to incompletely cure due to the presence of oxygen in these regions (oxygen is believed to inhibit curing of many lens forming compositions or materials). Uncured lens forming composition tends to result in lenses with xe2x80x9cwetxe2x80x9d edges covered by sticky uncured lens forming composition. Furthermore, uncured lens forming composition may migrate to and contaminate the optical surfaces of the lens upon demolding. The contaminated lens is then often unusable.
Uncured lens forming composition has been addressed by a variety of methods (see, e.g., the methods described in U.S. Pat. No. 5,529,728 to Buazza et al). Such methods may include removing the gasket and applying either an oxygen barrier or a photoinitiator enriched liquid to the exposed edge of the lens, and then re-irradiating the lens with a dosage of ultraviolet light sufficient to completely dry the edge of the lens prior to demolding. During such irradiation, however, higher than desirable levels of irradiation, or longer than desirable periods of irradiation, may be required. The additional ultraviolet irradiation may in some circumstances cause defects such as yellowing in the lens.
The low photoinitiator levels utilized in many ultraviolet curable lens forming compositions may produce a lens that, while fully-cured as measured by percentage of remaining double bonds, may not possess sufficient cross-link density on the lens surface to provide desirable dye absorption characteristics during the tinting process.
Various methods of increasing the surface density of such ultraviolet light curable lenses are described in U.S. Pat. No. 5,529,728 to Buazza et al. In one method, the lens is demolded and then the surfaces of the lens are exposed directly to ultraviolet light. The relatively short wavelengths (around 254 nm) provided by some ultraviolet light sources (e.g., a mercury vapor lamp) tend to cause the material to cross-link quite rapidly. An undesirable effect of this method, however, is that the lens tends to yellow as a result of such exposure. Further, any contaminants on the surface of the lens that are exposed to short wavelengths of high intensity ultraviolet light may cause tint defects.
Another method involves exposing the lens to relatively high intensity ultraviolet radiation while it is still within a mold cavity formed between glass molds. The glass molds tend to absorb the more effective short wavelengths, while transmitting wavelengths of about 365 nm. This method generally requires long exposure times and often the infrared radiation absorbed by the lens mold assembly will cause premature release of the lens from a mold member. The lens mold assembly may be heated prior to exposure to high intensity ultraviolet light, thereby reducing the amount of radiation necessary to attain a desired level of cross-link density. This method, however, is also associated with a higher rate of premature release.
It is well known in the art that a lens mold/gasket assembly may be heated to cure the lens forming composition from a liquid monomer to a solid polymer. It is also well known that such a lens may be thermally postcured by applying convective heat to the lens after the molds and gaskets have been removed from the lens.
An embodiment of an apparatus for preparing an eyeglass lens is described. The apparatus includes a coating unit and a lens curing unit. The coating unit may be configured to coat either mold members or lenses. In one embodiment, the coating unit is a spin coating unit. The lens curing unit may be configured to direct activating light toward mold members. The mold members are part of a mold assembly that may be placed within the lens curing unit. Depending on the type of lens forming composition used, the apparatus may be used to form photochromic and non-photochromic lenses. The apparatus may be configured to allow the operation of both the coating unit and the lens curing unit substantially simultaneously.
The coating unit may be a spin coating unit. The spin coating unit may comprise a holder for holding an eyeglass lens or a mold member. The holder may be coupled to a motor that is configured to rotate the holder. An activating light source may be incorporated into a cover. The cover may be drawn over the body of the lens curing unit, covering the coating units. The activating light source, in one embodiment, is positioned, when the cover is closed, such that activating light may be applied to the mold member or lens positioned within the coating unit. An activating light source may be an ultraviolet light source, an actinic light source (e.g., a light source producing light having a wavelength between about 380 nm to 490 nm), a visible light source and/or an infra-red light source. In one embodiment, the activating light source is an ultraviolet light source.
The lens forming apparatus may include a post-cure unit. The post-cure unit may be configured to apply heat and activating light to mold assemblies or lenses disposed within the post-cure unit.
The lens forming apparatus may also include a programmable controller configured to substantially simultaneously control the operation of the coating unit, the lens curing unit and the post-cure unit. The apparatus may include a number of light probes and temperature probes disposed within the coating unit, lens curing unit, and the post-cure unit. These probes preferably relay information about the operation of the individual units to the controller. The information relayed may be used to control the operation of the individual units. The operation of each of the units may also be controlled based on the prescription of the lens being formed.
The controller may be configured to control various operations of the coating unit, the curing unit, and the post cure unit.
Additionally, the controller provides system diagnostics and information to the operator of the apparatus. The controller may notify the user when routine maintenance is due or when a system error is detected. The controller may also manage an interlock system for safety and energy conservation purposes. The controller may prevent the lamps from operating when the operator may be exposed to light from the lamps.
The controller may also be configured to interact with the operator. The controller preferably includes an input device and a display screen. A number of operations controlled by the controller, as described above, may be dependent on the input of the operator. The controller may prepare a sequence of instructions based on the type of lens (clear, ultraviolet/visible light absorbing, photochromic, colored, etc.), prescription, and type of coatings (e.g., scratch resistant, adhesion promoting, or tint) inputted by an operator.
A variety of lens forming compositions may be cured to form a plastic eyeglass lens in the above described apparatus. Colored lenses, photochromic lenses, and ultraviolet/visible light absorbing colorless lenses may be formed. The lens forming compositions may be formulated such that the conditions for forming the lens (e.g., curing conditions and post cure conditions) may be similar without regard to the lens being formed. In an embodiment, a clear lens may be formed under similar conditions used to form photochromic lenses by adding a colorless, non-photochromic ultraviolet/visible light absorbing compound to the lens forming composition. The curing process for forming a photochromic lens is such that higher doses of activating light than are typically used for the formation of a clear, non-ultraviolet/visible light absorbing lens may be required. In an embodiment, ultraviolet/visible light absorbing compounds may be added to a lens forming composition to produce a substantially clear lens under the more intense dosing requirements used to form photochromic lenses. The ultraviolet/visible light absorbing compounds may take the place of the photochromic compounds, making curing at higher doses possible for clear lenses. An advantage of adding the ultraviolet/visible light absorbers to the lens forming composition is that the clear lens formed may offer better protection against ultraviolet/visible light rays than a clear lens formed without such compounds.
In an embodiment, a composition that includes two or more photochromic compounds may further include a light effector composition to produce a lens that exhibits an activated color that differs from an activated color produced by the photochromic compounds without the light effector composition. The activated color is defined as the color a lens achieves when exposed to a photochromic activating light source (e.g., sunlight). A photochromic activating light source is defined as any light source that produces light having a wavelength that causes a photochromic compound to become colored. Photochromic activating light is defined as light that has a wavelength capable of causing a photochromic compound to become colored. The photochromic activating wavelength band is defined as the region of light that has a wavelength that causes coloring of photochromic compounds. The light effector composition may include any compound that exhibits absorbance of at least a portion of the photochromic activating wavelength band. Light effector compositions may include photoinitiators, ultraviolet/visible light absorbers, ultraviolet light stabilizers, and dyes. In this manner, the activated color of a lens may be altered without altering the ratio and or composition of the photochromic compounds. By using a light effector composition, a single lens forming composition may be used as a base solution to which a light effector may be added in order to alter the activated color of the formed lens.
The addition of a light effector composition that absorbs photochromic activating light may cause a change in the activated color of the formed lens. The change in activated color may be dependent on the range of photochromic activating light absorbed by the light effector composition. The use of different light effector compositions may allow an operator to produce photochromic lenses with a wide variety of activated colors (e.g., red, orange, yellow, green, blue, indigo, violet, gray, or brown).
In an embodiment, an ophthalmic eyeglass lens may be made from an activating light curable lens forming composition comprising a monomer composition and a photoinitiator composition. The monomer composition preferably includes a polyethylenic functional monomer. Preferably, the polyethylenic functional monomer composition includes an aromatic containing polyether polyethylenic functional monomer. In one embodiment, the polyethylenic functional monomer is preferably an ethoxylated bisphenol A di(meth)acrylate.
The monomer composition may include additional monomers to modify the properties of the formed eyeglass lens and/or the lens forming composition. Monomers which may be used in the monomer composition include polyethylenic functional monomers containing groups selected from acrylyl or methacrylyl.
In another embodiment, an ophthalmic eyeglass lens may be made from an activating light curable lens forming composition comprising a monomer composition, a photoinitiator composition and a co-initiator composition. An activating light absorbing compound may also be present. An activating light absorbing compound is herein defined as a compound which absorbs at least a portion of the activating light. The monomer composition preferably includes a polyethylenic functional monomer. Preferably, the polyethylenic functional monomer is an aromatic containing polyether polyethylenic functional monomer. In one embodiment, the polyethylenic functional monomer is preferably an ethoxylated bisphenol A di(meth)acrylate.
The co-initiator composition preferably includes amine co-initiators. Preferably, acrylyl amines are included in the co-initiator composition. In one embodiment, the co-initiator composition preferably includes a mixture of CN-384 and CN-386.
Examples of activating light absorbing compounds includes photochromic compounds, UV stabilizers, UV absorbers, and/or dyes.
In another embodiment, the controller is preferably configured to run a computer software program which, upon input of the eyeglass prescription, will supply the identification markings of the appropriate front mold, back mold and gasket. The controller may also be configured to store the prescription data and to use the prescription data to determine curing conditions. The controller may be configured to operate the curing unit to produce the appropriate curing conditions.
In one embodiment, the lens forming composition may be irradiated with continuous activated light to initiate curing of the lens forming composition. Subsequent to initiating the curing, the lens forming composition may be treated with additional activating light and heat to further cure the lens forming composition.
In another embodiment, the lens forming composition may be irradiated with continuous activated light in a heated curing chamber to initiate curing of the lens forming composition. Subsequent to initiating the curing, the lens forming composition may be treated with additional activating light and heat to further cure the lens forming composition.
In another embodiment, a system for dispensing a heated polymerizable lens forming composition is described. The dispensing system includes a body configured to hold the lens forming composition, a heating system coupled to the body for heating the monomer solution, and a valve positioned proximate an outlet of the body for controlling the flow of the lens forming composition out of the body.
A high-volume lens curing apparatus includes at least a first lens curing unit and a second lens curing unit. The lens forming apparatus may, optionally, include an anneal unit. A conveyance system may be positioned within the first and/or second lens curing units. The conveyance system may be configured to allow a mold assembly to be transported from the first lens curing unit to the second lens curing unit. Lens curing units include an activating light source for producing activating light. Anneal unit may be configured to apply heat to an at least partially relive or relax the stresses caused during the polymerization of the lens forming material. A controller may be coupled to the lens curing units and, if present, an anneal unit, such that the controller is capable of substantially simultaneously operating the three units. The anneal unit may include a conveyor system for transferring the demolded lenses through the anneal unit.